Currently, information is displayed using assembled sheets of paper carrying permanent inks or displayed on electronically modulated surfaces such as cathode ray displays or liquid crystal displays. Printed information displayed in these manners cannot be changed. Devices that allow for the modification of information, such as electrically updated displays, are often heavy and expensive. Information may also be applied to sheet materials via magnetically written areas, for example, to carry ticketing or financial information. Such magnetically written data, however, is not visible.
Media systems exist that maintain electronically changeable data without power. Such system can be electrophoretic (E-ink), Gyricon, or polymer dispersed cholesteric materials. An example of such electronically updateable displays can be found in U.S. Pat. No. 3,600,060, which shows a device having a coated, then dried emulsion of cholesteric liquid crystals in aqueous gelatin to form a field-responsive, bistable display. U.S. Pat. No. 3,816,786 also discloses a layer of encapsulated cholesteric liquid crystal responsive to an electric field. The electrodes in the patent can be transparent or non-transparent and formed of various metals or graphite. It is disclosed that one electrode must be light absorbing, and it is suggested that the light absorbing electrode be prepared from paints containing conductive material such as carbon.
Fabrication of flexible, electronically written display sheets is disclosed in U.S. Pat. No. 4,435,047. A substrate supports a first conductive electrode, one or more layers of encapsulated liquid crystals, and a second electrode of electrically conductive ink. The conductive inks form a background for absorbing light, so that the information-bearing display areas appear dark in contrast to background non-display areas. Electrical potential applied to opposing conductive areas operates on the liquid crystal material to expose display areas. Because the liquid crystal material is nematic liquid crystal, the display ceases to present an image when de-energized, that is, in the absence of a field. A first flexible substrate is patterned which is coated. A second pre-patterned substrate is bonded over the coating.
U.S. Pat. No. 5,251,048 discloses a light-modulating cell having a polymer-dispersed chiral-nematic liquid crystal. The chiral-nematic liquid crystal has the property of being electrically driven between a planar state, reflecting a specific visible wavelength of light, and a focal-conic state, transmitting forward scattering light. Chiral-nematic liquid crystals, also known as cholesteric liquid crystals, potentially in some circumstances have the capacity of maintaining one of multiple given states in the absence of an electric field. Black paint can be applied to the outer surface of a rear substrate to provide a light-absorbing layer forming a non-changing background outside of a changeable display area defined by the intersection of segment lines and scanning lines. A first glass substrate is patterned. A second patterned glass substrate is fixable spaced from the first substrate. The cavity is filled with liquid crystal.
U.S. Pat. No. 6,025,952 discloses a sheet having a light sensitive layer that can be patterned to form conductors that respond to electrical signals to operate on a light-modulating layer. The light-modulating layer is polymer dispersed liquid crystal and the light patterned conductor layer is silver halide layer. A sheet made according to the invention requires a light exposure step and subsequent silver halide processing. Silver halide processing requires repeated chemical diffusion processes.
U.S. Pat. No. 6,236,442 discloses a display sheet with a metallic conductive layer over a light modulating layer. The conductive layer is formed by vacuum depositing a continuous metallic layer and laser patterning the metallic layer to form segment electrodes. However, vacuum deposited conductive layers are expensive and fragile.
U.S. Pat. No. 6,394,870 discloses directly depositing opaque conductive ink in an image wise pattern by screen-printing. Screen-printing is sensitive to ink formulation, adhesion and printing process parameters. The inks require secondary processes, such as heating or ultra-violet curing to set. The materials can contain polymeric binders that are personally and environmentally harmful. Screens utilizing this technology have limited life and require periodic cleaning. Such processes can take many seconds to deposit the material. It would be useful to provide environmentally safe materials with a fast, dry patterning process.
U.S. Pat. Application No. 2003/0174264 A1 discloses that polymer dispersed liquid crystal materials can be coated on photographic machinery as part of a multiple layer coating. Such coatings require subsequent application of conductors. It would be useful to apply a conductive coating simultaneous with the deposition of the polymer dispersed liquid crystal layer.